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Old 27-03-2012, 11:33 PM   #74
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Lightbulb Day arc

The arc passes through the zenith, resulting in almost no shadows at high noon.

Diagram showing the relationship between the zenith, the nadir, and different types of horizon. The nadir is opposite the zenith.

Shadows of the trees when the sun is directly overhead (at the zenith). This happens at solar noon if the tree's latitude equals the sun's declination at that moment.

The word "zenith" derives from the inaccurate reading of the Arabic expression سمت الرأس (samt ar-ra's) meaning “direction of the head”/"path above the head",It was incorrectly reduced to 'samt' ("direction") and imprecisely written as 'senit'/'cenit' by those scribes...

The nadir (from Arabic: نظير / ALA-LC: naẓīr; meaning "opposite") is the direction pointing directly below a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface there...The word is also used figuratively to mean the lowest point of a person's spirits, or the quality of an activity or profession.

The orientation of the Earth's axis and equator are not fixed in space, but rotate about the poles of the ecliptic with a period of about 26,000 years, a process known as lunisolar precession, as it is due mostly to the gravitational effect of the Moon and Sun on the Earth's equatorial bulge...

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